The present invention refers to a novel and improved photoelectrical bobbin feeler for detecting or discriminating the full and empty conditions of a textile bobbin, which bobbin feeler is provided with three optoelectrical devices. These optoelectrical devices may comprise a light source and first and second light sensors for receiving light emitted from the light source and specularly or diffusely, respectively, reflected from the bobbin, the optoelectrical devices having optical axes defining a scanning plane. The optoelectrical devices may alternatively comprise two alternately pulsed light sources and one light sensor.
There have been known to the art for quite some time weft or filling bobbin feelers for shuttle weaving machines which respond when the bobbin is empty or depleted of yarn winding, in which event the weaving machine is stopped. In order to improve the detection of the "bobbin empty" condition, bobbins have been provided with a reflecting layer, or further have been prepared with a retroreflector, such as "Scotchlite" tape (Minnesota Mining & Manufacturing Comp.).
The use of such bobbins in weaving mills complicates the operation of the looms and increases the costs of production. Thus, recently there has arisen a demand for bobbin feelers which also operate accurately with conventional unprepared weft bobbins. Preferably, such bobbin feelers should also be usable with the known prepared bobbins, such as the ones provided with "Scotchlite" tape.
A photoelectrical bobbin feeler designed for scanning unprepared weft bobbins is described and shown in U.S. Pat. No. 3,693,671. Therein, the optical axes of a D.C.-supplied light source and a first photocell form an obtuse angle, whereas the optical axis of a second photocell is arranged near the optical axis of the light source. The principle of the detection is based on the fact that a normal yarn winding reflects diffusely, whereas the surface of the depleted bobbin shows a distinctly specular reflection. That is the usual weft bobbins are provided with a gloss varnish as a protective layer causing a certain degree of specular reflection. On prolonged use of the weft bobbin, the varnish is worn and the bobbin surface delustered, such that the detection of the "bobbin empty" condition becomes critical or even impossible.
The bobbin feeler known from the aforementioned U.S. Pat. No. 3,693,671 cannot be used for scanning bobbins prepared with "Scotchlite" tape since the second photocell is located near the light source and therefore is energized by light reflected from the retroreflecting tape, and thus, is unable to detect light diffusely reflected from the bobbin which is its very function.
Further, in German Pat. No. 2,335,794 (Swiss patent No. 559,364, Belgian Pat. No. 802,542, U.S. Pat. No. 3,892,492) there is described an optoelectrical weft bobbin feeler which comprises two alternately pulsed directional light sources and a sensor for receiving light emitted by the light sources and reflected from a bobbin. This bobbin feeler affords a distinct improvement in the critical case of dull or mat bobbin cores, and moreover does not respond to ambient light.
In German patent publication No. 1,223,320 there is described a photoelectrical bobbin feeler cooperating with a weft bobbin provided with a specularly reflecting metallic sleeve. This bobbin feeler comprises only one light source and one photosensor each of which is associated with a polaroid screen or filter. This bobbin feeler may generally be used for bobbins having a specularly reflecting or gloss-varnished core, however, does not work with mat or delustered bobbin cores.
Extremely critical is the scanning of bobbins with mat or dull core and glossy yarn winding, such as fiber glass. In this case, the reflection properties of the wrapped and empty bobbin are so close to one another that a difference is difficult to detect. Even in this case detection of the "bobbin empty" condition is possible only if the dull bobbin core exhibits a certain amount of specular reflection, i.e. when the goniometric curve of the reflected light shows a distinct maximum.